This proposal requests support for the development of a new imaging technology allowing the creation of MASDA-X, Multi-element Amorphous Silicon Detector Array for X-rays, the first flat-panel, digital imaging system for x-ray fluoroscopy, MASDA-X arrays will consist of thin, flat panels having up to a 30 by 30 cm2 imaging surface. The imaging surface consists of a regular two-dimensional pattern of individual imaging pixels. Each pixel consists of a single hydrogenated amorphous-silicon photodiode coupled to a single polycrystalline-silicon field-effect transistor which allow the imaging array to be self-scanning. These pixels will be spaced at a pitch as fine as 100 microm. The MASDA-X arrays, when used in conjunction with phosphor screens and with readout electronics also to be developed in this project, will permit high signal-to-noise fluoroscopic imaging at high frame rates. The successful completion of this project will result in the creation of a replacement technology for the x-ray image-intensifier (XRII) systems which are currently the primary means for performing fluoroscopic imaging. This fundamental advance will revolutionize numerous aspects of fluoroscopy. Flat panel imagers will have a profile approximately the same as that of a film cassette. This tremendous compaction compared to XRII systems will lead to far less bulky an cumbersome equipment which will directly benefit physicians and other personnel in a variety of clinical environments. Besides offering high resolution, high signal-to-noise, digital images as well as the prospect of high portable fluoroscopic units, flat panel imagers will eliminate the problem of veiling glare and the detuning problems of XRII systems. In addition, they will be unaffected by stray magnetic fields, and will not suffer distortion thereby assisting quantitative analysis such as blood volume flow. Thus, quality-assured imaging free from veiling glare, distortion, and detuning will be possible. The solid-state nature of the imaging surface means that it may be designed in any clinically advantageous configuration (eg. 4:3 for chest imaging). Lastly, current developments in the flat panel technologies imply that considerably larger imaging panels, up to 60 by 60 cm2, are likely to be available before the end of the decade. Undoubtedly, this technology will result in improvement of existing and the creation of new radiologic techniques ultimately resulting in better care for patients.